The present invention relates to a method and apparatus for a non-contact measurement of a temperature of a body.
In non-contact measuring of a temperature originating from heat radiation of a body, which is not the same as body temperature, since the body need not be thermally equalized, a problem arises in that an ambient radiation can drastically falsify a result of the measurement. The problem, actually a problem of signal-to-noise ratio, becomes even more critical if temperatures to be measured lie only slightly above or below an ambient temperature, such as within several 100.degree. C.
In order to avoid the above noted problem, according to advantageous features of the present invention, a chopper means is provided for chopping or interrupting the heat radiation between the body and a temperature sensor, and at least one ambient temperature of a sensor on the side of the chopper means facing the sensor is taken into account in evaluating the temperature detected by the sensor.
By virtue of the fact that the heat radiation between the body and the temperature sensor provided is chopped up or interrupted, heat radiation pulses detected by the sensor are produced, an amplitude of which is provided by two heat radiation components, namely, by ambient radiation on the sensor side of the chopper means and by heat radiation on the side of the chopper means facing away from the sensor, which latter heat radiation is composed of the ambient irradiation at that location and radiation of the body the temperature of which is to be detected.
While the ambient radiation on the side of the chopper means facing away from the sensor cannot be separated from the body radiation but can be reduced to an insignificant amount by, for example, a selected minimum distance between the chopper means and the body, and is practically time-invariant, the ambient radiation on the sensor side of the chopper means presents a more serious problem, especially when considering its change in time as it occurs after actuation of the sensor and chopper means, due to the electrical feeds as well as, generally, by the output of the chopper means and the fact that the mounting elements for the sensor and chopper means define relatively small-volume spaces wherein temperature fluctuations result despite a stable larger-space temperature.
Due to the fact that at least one ambient temperature of the sensor on a side of the chopper means facing the sensor is considered or taken into account in the evaluation process, it is possible to effect a temperature measurement which represents solely the temperature for the body radiation even before the partial system on the sensor side of the chopper means has become thermally stabilized which may take, in dependence upon the structure, relatively long periods of time and independent of the temperature where the partial system finally stabilizes on.
Commercially available temperature sensors for non-contact measurement of heat radiation have been proposed with the sensor being disposed in a housing and constructed as finished components, usually, with an integrated amplifier. In this connection, the present invention further proposes to utilize as the one ambient temperature, a temperature of the sensor housing.
As can readily be appreciated, a heat radiation of the sensor housing directly affects the actual sensor which, for example, may be constructed as a semi-conductor chip and integrated into the housing.
A further source of heat radiation which should be considered is the chopper means. Due to the work performed by the chopper means, especially since it is a mechanically operated chopper means, it acts in the surrounding air as a Joule's brake. In this connection, in accordance with the present invention, it is further proposed to take into account, as one ambient temperature, the temperature caused by the work performed by the chopper means.
In accordance with further features of the present invention, the temperature of the sensor housing is feedback-controlled so that it is at a predetermined value and this approach can optionally also be done with regard to the temperature rise resulting from the work of the chopper means.
If the heat radiation is chopped or interrupted by a mechanically moved chopper means, such as, for example, a disc with radiation-impermeable and radiation-permeable segments, it is also possible in accordance with the present invention, to provide a sensor for sensing a temperature in a region of the travel path of the chopper means as an ambient temperature.
While the temperature can be predetermined by appropriate regulation or control means, due to the bulk of the mechanical chopper means, such a regulation for maintaining temperature equalization over the entire area at the chopper means will be relatively sluggish or slow. For this reason, in accordance with the present invention, it is proposed that the temperature measured by means of the sensor is corrected as a function of the temperature produced by the chopper means.
Preferably, in accordance with the present invention, a first signal, dependent upon the temperature produced by the work of the chopper means, is multiplied by a first coefficient and then the product is added to a second coefficient in order to obtain a second signal. A third signal, dependent upon the temperature detected by the sensor by the second signal is divided in order to obtain a fourth signal, and the fourth signal is added to the first signal in order to obtain a signal representative of a body temperature or body radiation.
Advantageously, the sensor output signal, prior to being further evaluated, is averaged over several chopper periods of operation of the chopper means in order to eliminate incidental fluctuations of the sensor output signal.
The above noted coefficients for correcting the sensor output signal, based on the temperature produced by the work of the chopper means, are preferably determined experimentally from at least two measurements, at predetermined body temperatures and respectively two values of the temperature produced by the work of the chopper means and supplied to a memory means.
As noted above, one can only consider representative body temperature if the body has been thermally equalized. On the other hand, temperature measurement of a body that has not been thermally equalized represents only the thermal energy content of a body volume element lying directly within the region of the measurement.
With the use of such temperature measurement, in order to obtain, in the case of relatively large bodies an indication of the thermal energy content of a maximally large volume element of the body, it is proposed in accordance with the present invention that the temperature measurement be conducted by a sensor in the zone of an already existing recess at the body or a recess that has been provided for this purpose in order to increase or enlarge a body volume element for the thermal energy content of which the temperature measurement is representative.
In accordance with the present invention, the recess may, for example, be an opening of a can or container to be measured as a body or, with bodies not provided with a recess, such as, for example, metal ingots, the recess may be provided such as in the form of, for example, a bore. In this manner, the above noted temperature measurement becomes representative for the thermal energy content of a substantially larger body volume element since the provided recess acts similarly to a structure exhibiting black body radiation, and emits a heat radiation corresponding to the heat content averaged over a relatively large adjoining volume.
If, for example, the body is moved relative to the sensor such as, for example, on a production line, in accordance with the present invention, a period of operation of the chopper means is selected to be shorter than the time span during which the geometric recess lies within the sensor measuring range so that, during such measuring period, an adequate number of measuring samples are available so as to enable averaging thereby eliminating random variables.
According to the present invention, an apparatus or arrangement for non-contact measurement of a temperature of a body is provided which includes a first temperature sensor means, a heat radiation chopper means connected in front of the heat input of the sensor means, and at least one further temperature sensor means disposed at least chopper means and adjacent the first temperature sensor means, and on the side of the first sensor with respect to the chopper means.
Preferably, according to the present invention, first temperature sensor or a further temperature sensor is thermally tightly coupled with a housing of at least one of the first temperature sensor and the chopper means. It is further proposed in accordance with the present invention to connect at least one additional temperature sensor as a pick up for a controlled variable into a temperature feedback control circuit for the temperature of a zone or area wherein the pick up is located.
To provide for a simple construction of the arrangement or apparatus of the present invention, it is proposed to use a mechanically moved chopper means such as, for example, a chopper disc, provided with a plurality of segments impermeable to heat radiation and segments permeable to heat radiation, with the temperature sensor or, respectively, a further temperature sensor, being arranged directly adjacent the path of movement of the chopper.
It has been determined that, especially when providing a mechanical chopper means, relatively large time periods of from one hour to several hours may elapse due to the frictional work to the surrounding air until the air, ambient in the chopper means and thus the heat radiation transmitted from the zone of the chopper means to the first sensor means, has reached a stable value.
Since it is extremely important in many applications to be able to perform representative measurements directly after connecting the arrangement or apparatus to power, the provision of an additional temperature sensor means as proposed by the present invention adjacent the travel path of the chopper means is extremely advantageous because, by correspondingly considering the time-variable temperature detected by the additional temperature sensor means for a measured result, it becomes inventively possible to effect a representative measurement as soon as immediately after the connection of the apparatus or arrangement to power.
Although, as noted above, the time variable behavior of the heat radiation may be eliminated by the provision of one or more feedback control circuits, as can readily be appreciated, the total overall expense for such an arrangement is relatively high particularly when considering that it is necessary to include, as temperature-adjusting members, heating and/or cooling elements such as Peltier elements and, as noted above, such control circuits have a relatively slow response time or are sluggish.
Provision of a feedback-control circuit may be basically eliminated by providing an evaluating unit such as, for example, a data processing unit for receiving the outputs of at least some of the temperature sensors and generating and transmitting at an output side an output signal representative of the body temperature.
Preferably, in accordance with the present invention, such an evaluating unit for the performance of calculations on the output signal of the additional temperature sensor disposed in a zone of the chopper means with an output signal of the first temperature signal for the body temperature may include a multiplication unit connected at on input to an input for the further temperature sensor at the evaluating unit, with a signal of an adjustable value being fed to the second input of the multiplication unit. The output of the multiplication unit may be fed to a summation unit, with an adjustable signal value being fed to the second input of such unit. The output of the first temperature sensor may be transmitted at the evaluating unit to a numerator input of a dividing unit, the denominator input of which is fed with the output signal of the summation unit. The output of the dividing unit as well as the output of the further temperature sensor may be transmitted to a further summation unit the output of which is connected to the output of the evaluation unit.
Additionally, in accordance with the present invention, storage elements may be provided for storing the signals of the adjustable values, with the storage elements being connected to second input of the multiplication unit and to the summation unit connected thereafter. In situations wherein, as noted above, a recess is provided in a body to be measured, and the body is moved relative to the temperature sensor, in accordance with the present invention, it is necessary to take into account certain criteria indicating when a temperature measurement with respect to the moving body takes place at a correct location, that is, in a region of the recess and also to provide an indication as to when the temperature measurement should not take place inasmuch as the recess is not located in a predetermined position. Preferably, this difficulty is solved by connecting, after the first sensor, a threshold-value-sensitive unit the output of which operatively connecting the output of the first sensor with the output of the arrangement or apparatus if the value of the sensor output signal lies above or below a predetermined value according to the threshold value.
Since, in a body provided with a recess such as described hereinabove, only its surface radiation is effective for measurement, as long as the recess is not located or disposed in the measuring range of the sensor and there is a sudden change once the recess enters the measuring range, the above noted threshold-value-sensitive unit makes it possible to detect the point in time when the aforementioned recess lies within the measuring range of the sensor.
Preferably, in accordance with the present invention, the sensor and threshold-value-sensitive unit are constructed so that a response is obtained to a predetermined change in the temperature or, respectively, radiation per unit of time, detected by the first sensor. Thus, changes in radiation and/or flanks trigger the measurement independently of the prevailing temperature levels.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings.